Practical applications of ultrasonic imagers have suffered from poor ultrasonic lenses. These lenses have poor ultrasound transfer characteristics that attenuate the ultrasonic signal and introduce ultrasonic aberrations. Additionally, ultrasonic imagers have used a coherent ultrasound source for insonification of the object. A coherent ultrasound source does not provide a high quality ultrasound image. The resulting image is "speckled", in a manner somewhat similar to an image obtained by a laser. Additionally, an ultrasonic imager requires a method of effectively coupling an ultrasonic lens to an ultrasonic sensor with low signal loss.
Ultrasonic sensors are used in a wide range of applications, particularly medical imaging. Acoustic arrays configured as a two dimensional array of sensors using integrated circuit technology have been developed. One such acoustic array, is disclosed in U.S. Pat. No. 5,483,963 to Butler et al., issued Jan. 16, 1996, wherein certain rights have been assigned to the assignee of the instant application. U.S. Pat. No. 5,483,963 is incorporated herein by reference. Butler et al. disclose a plurality of ultrasonic transducers arranged in a reticulated two dimensional array, each sensor having a first independent electrical connection, and each sensor having a second common electrical connection. An integrated circuit signal processing means for processing signals from the two dimensional array of ultrasonic transducers is connected to each one of the plurality of ultrasonic transducers at the first independent electrical connection.
While known ultrasonic systems are useful, their operation is sometimes impeded by cross talk interference transmitted from one ultrasonic transducer to another. Therefore, it is a motivation of the present invention to provide an improved ultrasonic image using a sensor that reduces such deleterious effects from cross talk.
Further, transmitter elements in an ultrasonic system require relatively high voltage. Therefore, known ultrasonic arrays comprise circuitry capable of operating under high voltage conditions. The use of such relatively high voltage precludes constructing electronic integrated circuits to operate both receiver and transmitter elements with low voltage CMOS integrated circuit technology. CMOS has inherent advantages of relatively small size and low power. Therefore, it is another motivation of the present invention to provide an ultrasonic system comprising a low voltage receiver array electronics having high voltage transmitter circuitry in the same integrated circuits.
Ultrasonic systems use an ultrasonic transducer to convert electrical energy into sound energy. The sound energy produced is directed at an object, such as biological tissue, or objects immersed in water. Objects in the ultrasonic wave path reflect ultrasonic signals back to the ultrasonic transducer with varying degrees of efficiency. The transducer detects sound that is reflected back to the transducer and provides signals that may be processed to produce an image of the object.
Ultrasonic transducers are provided in linear transducers or rectangular transducers, with an array of ultrasonic detectors and transmitters. A lens system is incorporated in the system to focus the ultrasonic signal on the detector.
The performance of ultrasonic transducer systems may be improved by increasing the amount of ultrasonic energy available to the ultrasonic detector. This may be accomplished with a more efficient lens system.
Ultrasonic lens systems suffer from aberrations caused by astigmatism, coma, spherical aberration and distortion. These aberrations reduce the ability of the ultrasonic imager to resolve fine detail and may render the imager unsuitable for a given application.
Accordingly, there is a need for an ultrasonic imager having a high efficiency lens incorporating an efficient sensor/lens interface with a quasi incoherent transmitter utilizing a low volume fraction transducer.